Wet web tensile tester

ABSTRACT

Apparatus for testing weak webs, such as wet webs of paper pulp, for tensile strength and elongation is provided having a relatively flat member for placement of a web specimen, two clamping members superimposed one above the other over the relatively flat member, the lower clamping member clamping one end of the specimen to the flat member and the other clamping member providing means to hold the other end of the specimen, a lifting arm means capable of lifting said other end of the specimen into position to be clamped over the upper clamping member. Means are provided to apply tension on the clamped specimen through the two clamping members and measure the tensile strength of the specimen web.

United States Patent [1 1 Dauth et al.

[ June 26, 1973 Filed:

WET WEB TENSILE TESTER Inventors: Marcel .I. Dauth, Hawkesbury,

Ontario; Uldis V. Valters, Brownsburg, Quebec, both of Canada Canadian International Paper Company, Montreal, Quebec, Canada Sept. 28, 1971 Appl. No.: 184,494

Assignee:

US. Cl. 73/95, 73/103 Int. Cl. G0ln 3/08 Field of Search 73/95, 103

References Cited UNITED STATES PATENTS 11/1966 Bendl 73/103 X 5/1959 Conti 73/95 3,674,221 7/1972 Riemersma 73/955 X Primary Examiner-Jerry W. Myracle Attorney-R. G. McClenahan ABSTRACT Apparatus for testing weak webs, such as wet webs of paper pulp, for tensile strength and elongation is provided having a relatively flat member for placement of a web specimen, two clamping members superimposed one above the other over the relatively flat member, the lower clamping member clamping one end of the specimen to the flat member and the other clamping member providing means to hold the other end of the specimen, a lifting arm means capable of lifting said other end of the specimen into position to be clamped over the upper clamping member. Means are provided to apply tension on the clamped specimen through the two clamping members and measure the tensile strength of the specimen web.

6 Claims, 8 Drawing Figures mimcumze mm 3.741. 005

sum; or 6 PATENTEU JUN 2 6 I975 SHEEHOOFG FIGS.

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sum 5 or e BACKGROUND OF THE INVENTION The present invention relates, in general, to an improved apparatus for testing relatively weak webs, such as paper pulp or news print in the wet state, to determine the tensile strength and elongation of the web at break. More particularly, the invention relates to an improved wet web testing apparatus which permits the testing of relatively weak webs to'determine their tensile strength and elongation at break without requiring manual handling of the web subsequent to its formation and prior to testing.

Testing of wet webs of paper pulp and other weak webs for their tensile strengths has become an important tool in the process of paper making. By determining the wet strength of the freshly formed web of pulp, it is possible for paper manufacturers to conduct research on the process of paper making and also to obtain better control and reproducibility in paper manufacture. The article by Andrews et al., Pulp and Paper Magazine of Canada, pp. 681-691 (August 1945), discusses the value of determining the wet strength of pulps in the paper making process. Stephens and Pearson in Appita, Vol. 23, No. 4 pp. 261-278 (January 1970), discuss the utility of wet web tensile strength evaluation in controlling the pulp and paper making processes. Brecht and Erfurt in TAPPI, Vol. 42, No. 12, pp. 959-968 (December 1959) discuss an instrument for determining the wet tensile strength and elongation at breaking point of various pulps and compositions and the effect of different treatments in pulp production on the tensile strength of the web of pulp produced. McCallum in Pulp and Paper Magazine of Canada, Vol. 58, pp. 232-240, 1957, discusses a wet web strength testing instrument for testing tensile strengths of webs and the results obtained with different samples produced under different circumstances.

Other wet web tensile testers are described in U.S. Pat. Nos. 2,893,24l-and 3,015,230.

While wet web tensile strength testing apparatus is known to' the prior art, the prior apparatus requires handling by hand of the test web by the operator in placing the web in the tester. This seriously impairs the accuracy and reproducibility of the results obtained. In most cases the apparatus of prior art is complex and relatively expensive. By means of the present invention there is provided a wet web testing apparatus in which the wet web is not handled or touched by hand from the time it is formed up to testing and a wide specimen of web, such as'4 inches wide, may be employed to improve the reproducibility of the results obtained. The apparatus of the present invention is inexpensive to manufacture and can be employed with standard commercially available sheet forming apparatus and tensile testing and recording equipment, such as the Instron tester, which provides a recorded chart showing the tensile. strength and elongation of the specimen at break. The apparatus of the invention may also be employed to measure the force required to peel the web specimen from the forming Fourdrinier wire or screen. The value of this information to the paper maker is discussed in the article by Andrews et al., supra. The apparatus of the present invention also measure the tensile strength and elongation at break of the web while it is in the vertical position, rather than in the horizontal position as required in many prior art apparatus and this improves the reproducibility of the test results. The apparatus of the present invention is especially suitable for routine repeated testing of webs of pulp or other substances in the wet condition.

SUMMARY OF THE INVENTION According to the present invention, there is provided a weak web or wet web tensile strength tester employing a rectangular test specimen or a wet web formed on a forming Fourdrinier wire or screen. The apparatus of the invention comprises a table to support the Fourdrinier forming wire having on it the wet web which was formed on the wire. Superimposed upon the table are two rolls placed one above the other. Means are provided for clamping one end of the wet web between the lower of the two rolls and the screen by the weight of the roll. By means of a suction box affixed to a movable arm, the other end of the web is lifted from the wire and above the upper of the two rolls and clamped thereon by a spring clamping means. Releasable brackets which had held the upper roll in place disengage and stress is applied on the specimen by tensile testing and recording apparatus known to the art capable of applying predetermined regular application of force. The stress and strain are recorded on a recording chart to measure tensile strength and elongation at break of the specimen.

At no time is it necessary for the operator to handle the wet web during or prior to determination of tensile strength and elongation. The web is tested for its tensile strength and elongation while in the verticalposition and the results obtained are highly reproducible.

BRIEF DESCRIPTION OF DRAWINGS The invention will be further described in connection with one preferred embodiment by reference of the more detailed description which will follow and the appended drawings, in which:

FIG. 1 is a perspective view of the tensile testing apparatus in its initial position prior to operation.

FIG. 2 is a perspective view of the apparatus showing the web specimen being tested for tensile strength.-

FIG. 3 is a front elevation of the apparatus showing the web specimen in dotted position while being tested.

FIG. 4 is a plan view of the apparatus taken generally along the plane 4-4 of FIGS. 1 and 3.

FIG. 5 is a plan view of the web specimen on the Fourdrinier wire before being raised to testing position.

FIG. 6 is a vertical sectional view of the apparatus taken generally along line 6-6 of FIG. 1 and shows in broken lines the suction arm in position to lift the end of the specimen for testing purposes.

FIG. 7 is a vertical section similar to FIG. 6 taken generally along line 7-7 of FIG. 2 showing the web specimen being lifted up into testing position and one end clamped into position above the upper roll.

FIG. 8 is a perspective view of web specimen as formed on the F ourdrinier wire with the template in position as it outlines the specimen.

DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT Referring to the drawings, the apparatus of the present invention includes a table 10 equipped to accommodate a circular Fourdrinier forming wire or screen 1 l of the type sometimes referred to in the art as a British Sheet forming wire, mounted on the frame 11a and desirably having a Twill weave 68 X 56, upon which the wet web 20 is formed in the sheet forming apparatus using the standard sheet forming procedure outlined in Canadian Pulp and Paper Association (CPPA) Standard Method C-4, (approved October 1940, revised May 1950). The specimen 20a is outlined within the web 20 by template 12, as shown in FIG. 8, desirably of the dimensions of 10.15 cm. wide by 10.4 cm. long, positioned onthe screen by positioning pins 13a and 13b which fit into holes 130 and 13d on the screen, respectively, prior to filling the cylinder of the sheet forming apparatus with the pulp slurry. After excess water is drained from the pulp through the screen, the template 12 is removed from the screen and the web is dried by suction (not shown) and blotting paper. The screen 11 with web 20 and rectangular specimen 20a defined within it by outline 20b is then mounted on table using two positioning pins 13c and 13f on table 10 which fit into holes 13c and 13d in the screen.

The table 10 is affixed by means of the arm 14 to the crosshead 15 (equipped with knob 19) of a continuous tensile testing and recording instrument of the Instron type (not shown) by bolts 16a, 16b and 160.

Superimposed over thetable 10 and the web specimen 20a, one above the other, is a lower roll 21 held in position by pins 22a, 22b, 22c, 22d and an upper roll 23 of shorter length than roll 21. Upper roll 23 is held in position until tensile measurement is to'be'made by movable brackets 24a and 24b. Bracket 24a is movably affixed to table 10 by means of arm 25a and 250 as shown in FIG. 3 and clamp 24b is affized to table 10 by means of arm 25b at 25d. Upper roll 23 is affixed to vertical arms 26a and 26b which are in turn affixed to cross arm 27. Brackets 24a and 24b have indentations 24c and 24d, respectively, which register with vertical arms 26a and 26b, respectively, as shown in FIG. 1. Cross arm 27 is affixed to connecting bolt 28 which can be screwed tight to cross arm 27 by means of nut 29 -"mounted on cross arm 27.The bolt 28 is connected to pin 30 which is in turn held to pin 31 by disconnecting means 32 having a removable peg33 which permits disconnecting the apparatus from th'e'upperarm 34 which forms part of the Instron continuous tensile testing and recording instrument (not shown).

Rolls 21 and 23 are each desirably about 2.6 cm. in

diameter and covered with Fourdrinier wire or screens to aid in clamping the specimen for testing.

Suction arm 40 is movably connected to linkage 17 the movement of the suction arm 40 to lift the specimen for testing.v

As shown at FIGS. 2, 3 and 7, the cross arm 27 is equipped with rod 49 having a spring tensioning means 50 and fitted at its lower end with a clamping bar 51 which provides a means for clamping the upper end of specimen 20a to upperv roll 23in a taut position as shown in FIG. 2. Rod 49 equipped with spring tensioning means 50 is fitted into position as shown in FIGS. 2, 3 and 7 after suction'arm 40 has lifted the specimen 20a into position over roll 23, otherwise it would block passage of arm 40 with suctionbox 42 over upper roll 23.

In the'operation of the apparatus the web 20 is first formed on the screen 11 by pouring a pulp slurry in the desired amount into the cylinder of the sheet forming apparatus (not shown). The rectangular specimen 20a within the circular web 20 is outlined by a template 12 which is affixed to the wire 11, prior to filling the cylinder, by means of positioning pins 13a and 13b, as shown in FIG. 8. After drainage of excess water the template 12 is removed and the sheet is dried by suction (not shown) and blotting paper. The web 20 and the specimen portion 20a at this stage of the procedure is shown in FIG. 5. Screen 11 with web 20, and specimen 20a circumscribed within it, is affixed on table 10 by means of two pins 13c and l3f placed in-holes 13c and 13d in the screen. Of course, other alternative means may be provided for placing the specimen on the apparatus.

Lower roll 21 is placed over one end of the specimen 20a to hold by its weight that end of the specimen rigidly in place. Suction arm 40 is then turned over moving linkage 17 as shown by the dotted lines in FIG. 6 to place the suction box 42 over one end of the specimen 20a. Suction is applied to the suction box 42 through the tube 43 and the suction arm is then moved back peeling the sample from the screen at a slow uniform rate as shown in FIG. 7 so. that the upper end of the specimen 20a is placed over the top of the-upper roll 23. Spring tensioning means 50 is then placed in position andreleased, placing the clamping bar 51 overthe upper edge of the topside of the upper roll 23 thereby fastening the upper end of the specimen 20a over upper roll 23. Movable brackets 24a and 24b are moved aside as shown in FIG. 2 and the apparatus is then in position to start the continuous recording chart and applied tension to the specimen. This is done by moving crosshead 15 downward until the specimen'20a i's'taut as shown in FIGS. 2 and 3 and stress is applied at a rate of about 1 cm. per minute until the specimen 20a breaks. The Instron recording chart records the maximum load and elongation at break. The ruptured specimen is then unclamped, weighed immediately and oven dried to determine moisture content and basis weight. The apparatus .is then ready to prepare and receive another specimen to determine its tensile strength and break at elongation. When it is desired to measure the tension necessary to peel the specimen 20a from the forming wire 11, this is done by starting measurement readings on the-Instron recording chart before specimen 20a is completely peeled from the wire l1, as shown in FIG. 7. The early portion of the recorded stress measurement or tension is that required to peel the specimen 20a 1 from the wire 11.

The results obtained with the apparatus of the invention are highly reproducible. Duplicate and triplicate runs with the same pulp show variation in tensile strength values of approximately 1- 4.5%.

The terms and expressions which have been employed are used as terms of description andnot of limitation, are there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. An apparatus for testing the tensile strength of relatively weak webs, which comprises a relatively flat member for placement of the web to be tested, two clamping members superimposed one above the other over said flat member, said clamping members providing means for clamping each end of the specimen web, and lifting means capable of lifting one end of the specimen web over the upper clamping member, said lifting means being rotatably connected to said apparatus by an arm, and means for applying tension to the two clamping members and thereby to the clamped specimen web.

2. An apparatus in accordance with claim 1, wherein the two clamping members are rolls.

3. An apparatus in accordance with claim 1, wherein the relatively flat member is in the form of a table with which the lower clamping member is in contact.

4. An apparatus in accordance with claim 1 wherein said lifting means comprises a rotating arm having a suction means at one end capable of lifting one end of a specimen web over the upper clamping member.

5. An apparatus in accordance with claim 1, wherein removable brackets are provided to hold the upper clamping member in place, said removable brackets being capable of holding said upper clamping member in place until tensile strength measurement is to be made.

6. An apparatus for testing the tensile strength of relatively weak webs, which comprises a table for placement of the web to be tested, two rolls superimposed one above the other over said table, said lower roll providng means for clamping one end of the specimen web to said table and said upper roll being provided with clamping means to hold the other end of the specimen web, and lifting means equipped with a suction source and being capable of lifting one end of the specimen web over the upper roll for clamping and means for applying tension to the two rolls and thereby to the clamped specimen web, said lifting means being rotatably connected to said apparatus by an arm. 

1. An apparatus for testing the tensile strength of relatively weak webs, which comprises a relatively flat member for placement of the web to be tested, two clamping members superimposed one above the other over said flat member, said clamping members providing means for clamping each end of the specimen web, and lifting means capable of lifting one end of the specimen web over the upper clamping member, said lifting means being rotatably connected to said apparAtus by an arm, and means for applying tension to the two clamping members and thereby to the clamped specimen web.
 2. An apparatus in accordance with claim 1, wherein the two clamping members are rolls.
 3. An apparatus in accordance with claim 1, wherein the relatively flat member is in the form of a table with which the lower clamping member is in contact.
 4. An apparatus in accordance with claim 1 wherein said lifting means comprises a rotating arm having a suction means at one end capable of lifting one end of a specimen web over the upper clamping member.
 5. An apparatus in accordance with claim 1, wherein removable brackets are provided to hold the upper clamping member in place, said removable brackets being capable of holding said upper clamping member in place until tensile strength measurement is to be made.
 6. An apparatus for testing the tensile strength of relatively weak webs, which comprises a table for placement of the web to be tested, two rolls superimposed one above the other over said table, said lower roll providng means for clamping one end of the specimen web to said table and said upper roll being provided with clamping means to hold the other end of the specimen web, and lifting means equipped with a suction source and being capable of lifting one end of the specimen web over the upper roll for clamping and means for applying tension to the two rolls and thereby to the clamped specimen web, said lifting means being rotatably connected to said apparatus by an arm. 